1. Field of the Invention
The present invention relates to devices for producing steam from liquid water, the steam being usable particularly in cooking appliances.
Numerous steam generators are already known which generally comprise an electric resistance immersed in a water reservoir. Supplying the electric resistance with electric energy produces a temperature rise of the water contained in the reservoir, then boiling and the escape of steam from the surface of the liquid.
These devices have the drawback of great inertia: before beginning to produce steam, it is necessary to heat the liquid contained in the reservoir, which requires a relatively long time; from the moment when the steam begins to be produced, if it is desired to stop the production of steam, the power supply to the electric resistance must be cut off; once the electric power supply is cut, the water contained in the reservoir is still at a high temperature and the production of steam continues for some time.
2. Description of the Prior Art
The document DE-A-3 532 261 describes a steam generating device comprising, in the embodiment shown in FIG. 3, a lower reservoir with a water intake device, an upper reservoir with a steam escape orifice and several heating riser tubes sealingly connecting together the two lower and upper reservoirs; a return tube also connects the two reservoirs together. Water level detection and regulation means, comprising a water level probe and a water supply pump, maintain the water level at an intermediate height in the upper reservoir, so that the lower reservoir and the heating tubes are entirely filled with water, as well as about half of the upper reservoir. The device described in this document, which contains a large amount of water, has the same drawbacks of thermal inertia as those mentioned in connection with the plunging resistance devices.
The document EP-A-0 238 955 describes a deep fryer having a structure relatively similar to that of document DE-A-3 532 261, with an upper reserve, a lower reserve, and heating tubes connecting them together. The liquid also fills the lower reserve, the whole of the heating tube and a part of the upper reserve, so that the drawbacks of thermal inertia and steam production are also present in this device.
Such a great inertia does not make it possible to accurately regulate the steam production. The result is that such known steam generators, which may be suitable for the production of saturated steam in large amounts, are no longer suitable when it is desired to regulate accurately the amount of steam produced, e.g. for producing non saturated steam in an enclosure under well defined conditions.
Furthermore, known steam generators have the drawback of containing, during their operation, a relatively large amount of water kept at a high temperature. This means that the lime contained in the water furs up all the parts of the device containing water, causing frequent breakdowns. In particular, the lime is deposited in inaccessible positions, difficult to clean and requiring long and expensive de-scaling operations.